Origin of Species - Chapter 24 Flashcards Preview

Biology 112 > Origin of Species - Chapter 24 > Flashcards

Flashcards in Origin of Species - Chapter 24 Deck (38):
1

What Darwin said about speciation

"mystery of mysteries"

Darwin believed that the process of natural selection could explain the diversity of life, given enough time. 

many definitions of speciation

2

Speciation, microevolution, macroevolution

speciation - the process of splitting one species into 2 or more

microevolution - change in allele frequencies in a population

macroevolution - broad pattern of evolution above the species level

3

Biological Species Concept

a definition of species that defines a species as a group that is able to produce healthy offspring with each other and can't do so with other groups

Speciation in this definition depends on reproductive isolation

speciation has occured when populations become reproductively isolated

4

Problems with Biological Species Concept

asexual organisms

extinct forms (what could they breed with? can't determine)

species that hybridize

ring species

It's difficult to apply this concept to the real world because many species that seem very different have gene flow betwen them.

5

Why is ambiguity in speciation expected?

nature seldom conforms to neat categories

new species often evolve gradually

not one point in time that you can identify as the moment of speciation

6

Reproductive isolating mechanisms

Prezygotic barriers to reproduction

prevent gene flow between populations
  1. habitat isolation - different species living in different habitats, but the same area, will rarely (if ever) encounter each other
  2. temporal isolation (gametes can't mix between species who breed during different seasons)
  3. behavioral isolation (courtship displays) - mate recognition doesn't occur between speices with different mating rituals, so they won't interbreed
  4. mechanical isolation (irish wolfhound&chinese crested dogs) - morphological differences don't allow successful mating
  5. gametic incompatibility (esp. for ext. fert. need to separate plants) - sperm can't fertilize egg of other species

7

Mechanisms for reproductive isolation

allopatric speciation

sympatric speciation

8

Prezygotic vs postzygotic barriers to genetic exchange

Prezygotic barriers stop fertilization from occuring

Postzygotic barriers contribute to reproductive isolation after a hybrid zygote is formed. 

9

Reproductive isolating mechanisms

Postzygotic barriers to reproduction

  1. reduced hybrid viability - mix of hybrid genes hinder survival and development
  2. reduced hybrid fertility - gametes don't align and produce sterile offspring (no gene flow)
  3. hybrid breakdown - hybrids are fertile, but their offspring are not.

10

Morpohological Species Concept

Based on appearance 

morph - shape

Linnaeus

concept relied on by paleontologists

11

Problems with morphological species concept

cryptic (sibling) speices - virtually identical, but don't interbreed

ecotypes - look different, but can interbreed

 

12

Allopatric Speciation

most common among animals

occurs when two populations become geographically separated (size of geographic barrier depends on the speices ability to move about)

decreased by gene flow, can be fast (20 years worms at Woods)

Natural seleciton, genetic drift, mutation increase

  1. populations become geographically isolated
  2. isolation reduces gene flow (not interbreeding)
  3. genetic divergence of 2 populations
  4. eventually results in reproductive isolation (new speices!) (even if they come into contact again, they can't interbreed)

13

Which mechanisms of evolutionary change increase genetic divergence of isolated populations?

Which tend to prevent divergence?

increase: mutations, natural selection, sexual selection, genetic drift

decrease: gene flow

14

Sympatric Speciation

speciation without geographical separation

Process: Polyploidy, habitat differntation, sexual selection.  Once one of these occurs, a new species will arise if the mechanism contintues

15

What factors can reduce gene flow to cause sympatric speciation?

Polyploidy, habitat differentiation, sexual selection

16

Polyploidy

mechanism of sympatric speciation

ploidy = number of sets of chromosomes

results from an increase in chromosome nubmer

common in plants, rare in animals

instant speciation - because chromosomes can't line up in meiosis (not same number)

results from non-disjunction of chromosomes during meiosis

17

Autoploidy

unreduced gametes in meiosis (supposed to halve, but didn't - doubles)

first documented by Hugo DeVries in primrose (several new species of primrose, bigger and larger)

18

Alloploidy

hybridization follwed by non-disjunction

different species breeding then 1 has autoploidy error

2 rare events, but not necessarily in the same generation

event that initates: 2 different species interbreed, then hybrid reproducing asexually

19

Hybrids have a low fitness reinforcement in hybrid zones - why unhealthy hybrids would cause selection for individuals that only mated with members of their own population?

unhealthy hybrids are going to cause selection for individuals that only mate with their own population because these offspring will likely survive, whereas the unhealthy hybrids will not survive long enough to produce more offspring or the offspring will also be unhealthy, so theis will reinforce reproductive barriers

20

"mystery of mysteries"

Darwin believed that the process of natural selection could explain the diversity of life, given enough time. 

many definitions of speciation

What Darwin said about speciation

21

speciation - the process of splitting one species into 2 or more

microevolution - change in allele frequencies in a population

macroevolution - broad pattern of evolution above the species level

Speciation, microevolution, macroevolution

22

a definition of species that defines a species as a group that is able to produce healthy offspring with each other and can't do so with other groups

Speciation in this definition depends on reproductive isolation

speciation has occured when populations become reproductively isolated

Biological Species Concept

23

asexual organisms

extinct forms (what could they breed with? can't determine)

species that hybridize

ring species

It's difficult to apply this concept to the real world because many species that seem very different have gene flow betwen them.

Problems with Biological Species Concept

24

nature seldom conforms to neat categories

new species often evolve gradually

not one point in time that you can identify as the moment of speciation

Why is ambiguity in speciation expected?

25

prevent gene flow between populations
  1. habitat isolation - different species living in different habitats, but the same area, will rarely (if ever) encounter each other
  2. temporal isolation (gametes can't mix between species who breed during different seasons)
  3. behavioral isolation (courtship displays) - mate recognition doesn't occur between speices with different mating rituals, so they won't interbreed
  4. mechanical isolation (irish wolfhound&chinese crested dogs) - morphological differences don't allow successful mating
  5. gametic incompatibility (esp. for ext. fert. need to separate plants) - sperm can't fertilize egg of other species

Reproductive isolating mechanisms

Prezygotic barriers to reproduction

26

allopatric speciation

sympatric speciation

Mechanisms for reproductive isolation

27

Prezygotic barriers stop fertilization from occuring

Postzygotic barriers contribute to reproductive isolation after a hybrid zygote is formed. 

Prezygotic vs postzygotic barriers to genetic exchange

28

  1. reduced hybrid viability - mix of hybrid genes hinder survival and development
  2. reduced hybrid fertility - gametes don't align and produce sterile offspring (no gene flow)
  3. hybrid breakdown - hybrids are fertile, but their offspring are not.

Reproductive isolating mechanisms

Postzygotic barriers to reproduction

29

Based on appearance 

morph - shape

Linnaeus

concept relied on by paleontologists

Morpohological Species Concept

30

cryptic (sibling) speices - virtually identical, but don't interbreed

ecotypes - look different, but can interbreed

 

Problems with morphological species concept

31

most common among animals

occurs when two populations become geographically separated (size of geographic barrier depends on the speices ability to move about)

decreased by gene flow, can be fast (20 years worms at Woods)

Natural seleciton, genetic drift, mutation increase

  1. populations become geographically isolated
  2. isolation reduces gene flow (not interbreeding)
  3. genetic divergence of 2 populations
  4. eventually results in reproductive isolation (new speices!) (even if they come into contact again, they can't interbreed)

Allopatric Speciation

32

increase: mutations, natural selection, sexual selection, genetic drift

decrease: gene flow

Which mechanisms of evolutionary change increase genetic divergence of isolated populations?

Which tend to prevent divergence?

33

speciation without geographical separation

Process: Polyploidy, habitat differntation, sexual selection.  Once one of these occurs, a new species will arise if the mechanism contintues

Sympatric Speciation

34

Polyploidy, habitat differentiation, sexual selection

What factors can reduce gene flow to cause sympatric speciation?

35

ploidy = number of sets of chromosomes

results from an increase in chromosome nubmer

common in plants, rare in animals

instant speciation - because chromosomes can't line up in meiosis (not same number)

results from non-disjunction of chromosomes during meiosis

Polyploidy

mechanism of sympatric speciation

36

unreduced gametes in meiosis (supposed to halve, but didn't - doubles)

first documented by Hugo DeVries in primrose (several new species of primrose, bigger and larger)

Autoploidy

37

hybridization follwed by non-disjunction

different species breeding then 1 has autoploidy error

2 rare events, but not necessarily in the same generation

event that initates: 2 different species interbreed, then hybrid reproducing asexually

Alloploidy

38

unhealthy hybrids are going to cause selection for individuals that only mate with their own population because these offspring will likely survive, whereas the unhealthy hybrids will not survive long enough to produce more offspring or the offspring will also be unhealthy, so theis will reinforce reproductive barriers

Hybrids have a low fitness reinforcement in hybrid zones - why unhealthy hybrids would cause selection for individuals that only mated with members of their own population?